1. Field of the Invention
This invention relates to a method of and a system for producing a solid model, wherein an incomplete wire frame model representative of an external shape of an object is corrected to make a complete wire frame model, based on which closed loops composed of respective arcs or feature-lines of the external shape of the object are determined, and respective closed loops and curved surfaces prepared in advance are matched.
2. Description of the Related Art
In designing a vehicle body, conventionally, a mock-up model representative of the vehicle body is first produced. Then, a wire frame model is produced by extracting feature-lines existing on the external surface of the mock-up model as arcs, and dividing the external surface into a set of curved surfaces, ie three-dimensionally curved surfaces, along the arcs. The arcs looping around each curved surface form a closed loop (called a "surface loop"). A solid model, ie a three-dimensional model (called also a "surface model") is built by connecting such curved surfaces, based on data (called "NC data") input to a numerically controlled machine tool for fabricating a press mold is produced.
In the situation described above, since the mock-up model has often been produced putting a greater importance on design than others, there may be a case where the mock-up model is not accurate in terms of details. Thus, there may be included defective arcs whose end points do not meet at any of nodes in a wire frame model created by a CAD system based on such an inaccurate mock-up model. In such a situation, the NC data cannot be obtained immediately from an incomplete wire frame model.
Thus, in the customary practice, when an operator inspected CAD data about a wire frame model and found an imperfection such as an arc having no endpoint at which it intersects with another arc, such an imperfection had to be corrected to obtain a complete wire frame model during a conference of the CAD operator and a producer of the mock-up model.
The customary method mentioned above, however, has been time consuming, especially when the wire frame model includes many surface loops representing a complex external shape of a vehicle body. Further, there have been problems that the time required for the model correction and the accuracy of the resulting model are different depending on the degree of experience of the operator in charge.